1. Field of the Invention
This invention generally relates to digital recording systems, and more particularly to a method and apparatus for synchronizing audio and video frames received in digital television and/or digital video recording (DVR) systems.
2. Description of Related Art
In general, digital video and audio signals can be broadcast, processed, and recorded with a high degree of quality. In order to take better advantage of the high quality associated with digital video/audio, digitally-based peripheral devices, such as digital video cassette recorders (DVCR's) and digital video disks (DVD's), have been developed to receive and process video/audio in a digital format. Systems employing such devices receive broadcast entertainment-type data, such as packetized digital video, audio, data, and control signals received in a direct broadcast satellite (DBS) system, and effectively record the received data on a device such as a digital video recorder (DVR).
Within these packetized transport streams, or transport packets, resides data that, when de-multiplexed by the user or subscriber, transforms into a group of pictures, or GOP. A GOP consists of coded pictures. A coded picture may be a frame or field. Current digital video recorders (DVRs) include some type of transport processor to process received transport packets from any of a cable, satellite, video-on-demand or other broadcast source. Known as a transport packet processor or simply “transport processor”, the transport processor is typically required to perform real-time functions and operations such as conditional access, program guide control, etc.
One particular function of transport processor software is to use the software, working in tandem with an MPEG decoder, to ensure that audio and video frames are synchronized prior to being displayed for either a live broadcast, or a recorded event, program or broadcast on a suitable display device such as an HDTV, video monitor, etc.
AV synchronization cannot be achieved for live and playback modes without the use of additional hardware components. In a typical digital broadcast system, AV synchronization is achieved by using a System Clock Reference (SCR). The SCR is frequently embedded in the data stream and in a corresponding time stamp (TS) when the SCR is received by the system. Typically, the TS must be latched through a hardware component handling the transport stream. Therefore, for proper AV synchronization of a recorded event, these SCR and TS values are also required to be recorded, in addition to the entertainment content. This is so an inter-arrival time between the packets that are to be recorded is maintained. This adds to complexity of the system, as well as to the cost, since greater storage is required. This may result in slower system processing time. Moreover, if each frame does not have a corresponding SCR and TS therein, or the SCR and/or TS is not properly recorded, processing of these audio and video frames of the displayed program or event may create errors, such as a program where the audio portion lags or leads the corresponding video portion. Such is undesirable whether watching live or recorded content.